Device and process for magnetic material detection in electronic article surveillance (EAS) electromagnetic systems

Abstract

The present invention relates to a device with its related electronic circuit and to a detection process targeted to detect any magnetic material moving around the antennas/sensors used in Electronic Article Surveillance (EAS) electromagnetic systems, which can be internally or externally coupled to these kind of anti-theft systems, significantly decreasing its current vulnerability to fraud since the current EAS electromagnetic systems are vulnerable for not being able to detect magnetic materials. The present process and detector device filter and treat the DC signal generated by the displacement of a magnetic material around one or more EAS electromagnetic system antenna/sensor(s). Magnetic material detection is achieved from a differential signal existing in the antenna/sensor receiver, such signal being forwarded to a control unit wherein there are coupled a device comprising a “n” order filter, a buffer, a sensitivity control circuit, a control logic and an alarm module.

1. A device for magnetic material detection coupled to an Electronic Article Surveillance (EAS) electromagnetic system, the system being comprised of:
 at least one antenna/sensor ( 6 ) for detecting EAS tags different from the magnetic material and generating a differential signal responsive to an EAS tag; and 
 a control unit ( 7 ); 
 characterized in that the device comprises: 
 an “n” order filter ( 1 ) wherein n is an integer, 
 a buffer or a high impedance insulator circuit ( 2 ), 
 a sensitivity adjuster or gain control circuit ( 3 ), 
 a control logic ( 4 ), and 
 an alarm module ( 5 ), 
 wherein the filter ( 1 ), the buffer ( 2 ), the sensitivity adjuster or gain control circuit ( 3 ), the control logic ( 4 ) and the alarm module ( 5 ) are compatibly internally or externally coupled to the EAS electromagnetic system; 
 the control unit ( 7 ) receives a differential signal detected from the antenna/sensor ( 6 ) representative of the EAS tag and the magnetic material, and internally or externally forwards it to the “n” order filter ( 1 ); 
 the output of the “n” order filter ( 1 ) is a signal presenting both AC and DC component information, this signal is sent to the buffer or high impedance insulator circuit ( 2 ), which buffers the previous stages to avoid harm in the EAS tag detection and filters out the DC component, which DC component is then processed by the sensitivity adjuster or gain control circuit ( 3 ) and given to the control logic ( 4 ) for digital filtering; and 
 the control logic ( 4 ) output from the digital filtering is connected to the alarm module ( 5 ) for generating an alarm when said magnetic material is detected. 
 
     
     
       2. A device according to  claim 1 , characterized in that the EAS electromagnetic system comprises two antennas/sensors. 
     
     
       3. A device according to  claim 1 , characterized in that the EAS electromagnetic system comprises four antennas/sensors forming two pairs, the first of the pairs employed as the EAS electromagnetic system proper, and the other used to detect magnetic materials, regardless of the position of these two pairs. 
     
     
       4. A device according to  claim 1 , characterized in that the sensitivity adjuster or gain control circuit ( 3 ) adjusts the magnetic material detection as well as equalizes its response to the signal level from the “n” order filter ( 1 ). 
     
     
       5. A device according to  claim 4 , characterized in that the sensitivity adjusted by the sensitivity adjuster or gain control circuit ( 3 ) varies in function of the “n” order filter ( 1 ) response, the magnetic material mass or surface, the magnetic material composition, the environment electromagnetic noise, the influence of metallic masses as well as the antennas/sensors ( 6 ) impedance. 
     
     
       6. A device according to  claim 1 , characterized in that the alarm module ( 5 ), in case of a magnetic material detection event, turns on electromechanical, audible, visible and/or electronic devices, all from the group of audible alarms, visible alarms, remote actuation of electric locks, turnstiles, and voice synthesizers. 
     
     
       7. A process for magnetic material detection by a device coupled to an EAS electromagnetic systems, wherein when a magnetic material approaches antennas/sensors ( 6 ) of said EAS electromagnetic system, a differential signal resulting in an antennas/sensors ( 6 ) receiver element connected to the antennas/sensors ( 6 ) presents a new component as a result of the magnetic material displacement through the space existing between the antennas/sensors ( 6 ), characterized by further comprising the steps of:
 obtaining a disturbing DC field from the differential signal existing in the antennas/sensors receiver element of the EAS electromagnetic system, wherein said disturbing DC field overlaps an AC field resulted from presence of an EAS tag that is used for EAS tag detection, and the DC field is generated when said magnetic material passes through the space or area existing between the antennas/sensors of the EAS electromagnetic system, and wherein when displaced, the magnetic material also causes a very low frequency amplitude modulation on said differential signal; and 
 filtering and processing said disturbing DC field, wherein the magnetic material is detected when said disturbing DC field is present in said differential signal. 
 
     
     
       8. A process according to  claim 7 , characterized in that the magnetic material detection occurs simultaneously with EAS tag detection. 
     
     
       9. A process according to  claim 7 , characterized in that the magnetic material detection occurs during the displacement of said magnetic material. 
     
     
       10. A process according to  claim 7 , wherein the device is coupled to the EAS electromagnetic system either internally or externally, characterized in that the magnetic material detection occurs in one pair of antennas/sensors ( 6 ) of the EAS electromagnetic system, in case of internal coupling; and the magnetic material detection occurs in another pair of antennas/sensors ( 6 ) used only for magnetic material detection, in case of external coupling, regardless of the position of these two pairs.